Historically, cataract surgery has been performed using ultrasonic handpieces providing a longitudinal or “jackhammer” like motion at a tip of a needle received by the handpiece. High-powered longitudinal mode ultrasonic handpieces used in cataract surgery typically consist of the components depicted in FIG. 1. The surgical needle threads into a stepped horn which is ultrasonically driven by a stack of piezoelectric ceramic elements. A spacer is located behind the stack of ceramic elements. A rear mass with a mount, isolation tube and Luer connector threads onto a center bolt which passes through the stack. When torqued, the rear mass applies a compressive pre-load to the stack. A lumen for aspiration of fragmented cataract tissue passes through the needle into the horn, through the center bolt and into the rear mass, exiting the Luer connector and passing into a flexible tube which is attached to a pump. O-ring bore seals, one located behind the horn step and the other in the rear mount, provide a water tight barrier for the handpiece inside its housing.
With longitudinal mode handpieces, cutting only occurs for the half of the oscillation cycle during which the needle tip advances toward the cataract. For the half of the cycle during which the needle tip moves away from the cataract, the needle tip is not cutting, but energy is required and heat is generated throughout the entire cycle. As a result, cutting efficiency is not optimized and cutting time is increased.
Torsional mode phacoemulsification was introduced by Alcon, Inc. in 2006 in the form of the OZil® handpiece depicted in FIG. 2. The OZil® handpiece delivers both longitudinal and torsional motion to the needle, which, depending upon the tip geometry, cuts in either a rotating or transverse shearing motion. Longitudinal vibration generated by the stack is partially converted to torsional motion by a torsional spring integrally machined into the horn of the OZil® handpiece depicted in FIG. 2. A bent tip needle with a Kelman configuration amplifies the shaft torsion through a side-to-side pivoting motion at the tip while a needle with a straight or flared tip cuts with a rotational motion amplified by the distance from the center of the needle to the outermost cutting edge of the tip.
When the needle tip is moving transversely or rotationally in torsional mode, more edge is applied to cutting as opposed to repulsing the cataract, and the needle tip maintains contact with the cataract throughout the cycle to cut more efficiently than purely longitudinal mode handpieces.
An improvement on the OZil® handpiece is described in U.S. Pat. No. 8,395,299 (Bromfield). Unlike the OZil® handpiece, in which the spring partially converting longitudinal motion to torsional motion is integral with the horn, the Bromfield design incorporates the spring into the handpiece as a discrete component. This significantly enhances design flexibility by facilitating alternative configurations and alternative spring materials to achieve different performance objectives.
U.S. Pat. No. 5,935,096 (Barrett) discloses needles used for emulsifying and removing the eyes lens during cataract surgery. A sleeve is arranged to surround the needle, and irrigant (i.e. liquid coolant) is fed to the surgical site through the space between the inner wall of the sleeve and the outer surface of the needle to reduce the risk of heat damage to the eye. In various embodiments, grooves are formed in the outer surface of the needle to provide channels by which the irrigant flows to the surgical site even when the entry wound compresses the sleeve against the outer surface of the needle. The shape, number and dimensions of the grooves do not matter so long as they provide a pathway for the irrigant to reach the internal chamber of the eye when the sleeve is compressed. In one embodiment shown at FIG. 5, the needle has multiple parallel helical grooves extending along the length of the outer surface of the needle shaft. The specific dimensions of the helical grooves are not discussed, and conversion of longitudinal drive motion to torsional motion at the needle tip is not described.
U.S. Patent Application Publication No. 2006/0047254 A1 (Akahoshi). also discloses several different embodiments of a needle used for emulsifying and removing the eye lens during cataract surgery. One of the embodiments, illustrated at FIG. 9a, has multiple parallel helical grooves extending along the length of the external surface of the needle shaft. Similar to the Barrett patent discussed above, the Akahoshi patent application is concerned with prevention of overheating at the surgical wound site. The Akahoshi patent application, unlike the Barrett patent, seeks to reduce heat generation without an outer sleeve (although a sleeve may also be used). Akahoshi discloses that from three to as many as five parallel helical grooves having a pitch angle in a range from 3° to 30° will generate a “reflux” flow of irrigant when the needle is used without a sleeve. The disclosure suggests that reflux is aided by using rounded or semicircular grooves that smoothly diminish in depth approaching the both ends of the groove. The specific dimensions of the helical grooves are not discussed, and conversion of longitudinal drive motion to torsional motion at the needle tip is not described.